texts: The consequences and the mechanisms of a shift of the Earth away from the sun

texts:
First premise: I have already made this question in the worldbuilding section, but since it is a very specific question many have recommended me to write in the astronomy section so here we are.

Second premise: I'm Italian so please excuse any mistake

So, I'm writing a story about a fast and cataclysmic climate change. Obviously there are some artistic licenses but I would like nothing in my story to be completely impossible, only (at most) very unlikely.

The climate change that I would like to include in my story is very extreme, so I had to discard any terrestrial forcing to cause it (no change of ocean currents, supervolcanoes and methane eruptions) because they could not act fast enough and would not be so catastrophic (compared to what I imagine). So I focused on astronomical forcing. I excluded the impossibly forcing (for example, a magical and radical reduction in solar luminosity) and those that would be more catastrophic than the climate change itself (i.e. a planetary impact).

The last possible (though very very unlikely) option I have left is a dramatic change in the Earth's orbit. I have some knowledge in physics and astronomy so I did a personal search to figure out what could cause such an orbital change.The most plausible option would be to pass a rogue planet (or star) into the solar system, but since I want to complicate my life, I would like the orbital change to happen without any notice, which is quite impossible if it is the passage of a planet or a star in the solar system to cause it.

The only plausible explanations I have found to fully satisfy my scenario are either the passage of a primordial black hole in the solar system (a black hole with Jupiter's mass would have a schwarzschild radius of 2.8 meters and, if it did not come in direct contact with some celestial body, it may take in the solar system without notice) or passing a high-density cluster of dark matter (assuming an self-interacting form of dark matter) near or inside the solar system. Both are immensely unlikely options and very speculative (primordial black holes are hypothetical objects and we still have no idea what the dark matter really is and how it behaves) but I do not think they are impossible in the beginning, or is it wrong?

Assuming I want to move the Earth 2x10^7 km (if I do not mistake at this distance the average temperature of the planet would be between 15 and 18 ° C lower than now) farther from the sun, could this change take place in less than a decade and the earth's orbit would remain stable or simply the planet would be expelled from the solar system?

I also wondered what effects this sudden and drastic lowering of the Earth's temperature would have on the weather (especially considering that the poles would cool down much faster than the equator) but I think it's a pretty OT question so I leave it as optional


texts: Exposure time for spectroscopy compared to photometry

texts: For a report I'm writing, I'm interested in comparing the exposure time required for spectroscopy versus photometry for a given magnitude. I found the figures on pages 7 and 8 of this lecture particularly informative. I tried emailing the author, but his email address is inactive. Where can I get similar information?


texts: What constellations touch the 9-degree wide Zodiac?

texts:
Say Barry, could you abuse the answer-your-own-question feature of
this site, and answer the following question:

As noted in How many constellations in the Zodiac? the
ecliptic itself touches 13 constellations, but the Encylopedia
Brittanica defines the Zodiac as "a belt around the heavens extending
9 [degrees] on either side of the ecliptic":

http://www.britannica.com/topic/zodiac

The Old Farmer's Almanac for 2014 (and previous years) notes (page
114) that Moon occasionally crosses into 5 "non-Zodiac" constellations
at times:

So, exactly which constellations are "in the Zodiac" if the Zodiac
extends 9 degrees on either side of the ecliptic?

And why 9 degrees? I know Venus can be as much as 8.25 degrees from
the ecliptic,


texts: What is the furthest star for which we can measure the diameter?

texts:
If a star is close enough that we can measure its parallax and that it doesn't appear point-like, then we can deduce its diameter. Can we measure the diameter of all the stars for which we can measure the parallax, or is the angular diameter a limiting factor?
How far out is the diameter of a star measurable?


texts: Correction to inverse square law for cosmology

texts:
While reading about the discovery of quasars and the spectroscopic analysis of 3C 273 in this paper by Maarten Schmidt, I came across the following quote:

  At these distances, corrections to luminosities depend on the specific world model. For
  an approximate determination of the fluxes in the emission lines we use the formulae
  given by Sandage (1961) based on Mattig (1958). For the energy contained within an
  emission line, in which we integrate over the entire profile, the correction to the inverse square law is of the form $(1 + z/2)^2$
  if the cosmological constant and deceleration parameter are zero. It is $(1 + z)^2$
  for the steady-state model.

First, why is a correction to the inverse square law necessary? Is it to do with interstellar extinction?

Second, why are the two models different? I understand what the cosmological constant and deceleration parameter are, but why is the redshift prediction for a steady state model twice as much as when $\Lambda=q=0$?


texts: Accretion disks - why are they disk-shaped, rather than spherical?

texts:
So, the theory (briefly) about accretion disks is that stuff falling into the black hole will most likely not fall straight into it but will miss it and go into orbit, perhaps for a long time, perhaps for a short time, before finally falling in.  That makes sense.

But, why disks?  Wouldn't the matter falling into the BH be coming from all directions, and thus fall into orbits in all planes around the BH, not just one?  Or, is it that once there's a hint of "plane preference" in the debris, this will tend to be self-reinforcing, and anything subsequently falling into orbit around the BH will hit something in the disk, and so end up (perhaps after many collisions) being swept around in the disk as well?


texts:
The cycle of solar maximums and solar minimums are each about 11 years, which is close to the orbital period of Jupiter. I thought it was a numerical coincidence, until google turned up some results of a possible connection. A lot of it is beyond my head though.

I was under the impression that there are gaps in our knowledge regarding Jupiter's core, which would likely be the driver of its magnetic field. And since solar cycles are related to sunspot activity, which in turn is related to the magnetic field of the Sun, I am struggling to find even a basic understanding of the cause-effect relationship (if there is one).

Is there a connection between Jupiter's orbital period and the Sun's solar cycles? Or is it blind speculation?


texts: What's the origin and culture of funny astronomical terminology?

texts:
I'm not in the industry myself, but as an interested member of the public the terminology of astronomy seems a bit funny. Astronomers who today talk publicly about the interstellar medium say that the solar system is in the "local fluff" inside the "local bubble" near a "local chimney". Cosmology uses a term like "the dark ages" to describe an era in the history of the phenomena they study. But geologists instead prefer to use terms like "cenozoic" to name a period. Early on, astronomers also used pompous words and names from antique languages.

Was "Big Bang" (coined in 1949, I think) the term which started off this fluffy bubble blob bang type of terminology? Or were there precursors?
Is there a connection to sci-fi literature?
Are the "blobby bang fluff" words just a mass media ("reach out") construction which professional astronomers don't use at all even as quick references in conversations with colleagues?


texts: Are mass extinction events more likely during meteor showers / passing through comet debris?

texts: Meteor showers happen when Earth passes through the debris left by a comet in its orbit. Meteors are generally tiny, like snow flings or pebbles and don't make it to the ground as meteorites. But periodic comets sublimate and disintegrate. Don't they shed kilometer sized fragments too? Maybe it is not only the comet which is the threat, but its entire orbit is a minefield too? Are bolides and observed meteorite falls more frequent during meteor showers?


texts: Are these stars in MASCOT image of Ryugu?

texts:
Are these stars in this MASCOT image of Ryugu?

Larger image:
https://www.sciencealert.com/images/2019-08/processed/RocksOfRyuguStranglyFamiliar_1024.jpg

They seem too bright to be stars (if the foreground is sunlit) and there are similar bright spots in shadowed areas of Ryugu.

Famously  there are no stars visible in Apollo Moon photos:

  the picture you take is set for bright objects. Stars are faint objects! In the fast exposure, they simply do not have time to register on the film. It has nothing to do with the sky being black or the lack of air, it's just a matter of exposure time. If you were to go outside here on Earth on the darkest night imaginable and take a picture with the exact same camera settings the astronauts used, you won't see any stars!
  Phil Plait, Bad Astronomy

Ryugu has half the albedo of the Moon, but that shouldn't make much difference.

@AtmosphericPrisonEscape suggests they may be dust particles as seen on Comet 67P.  However, the second video in this article shows that there are also stars in the 67P images. I can't tell whether the comet surface is in direct sunlight or reflected light.  Also, I don't know the dimensions of the parts of 67P and Ryugu depicted.

Paul Byrne
(@ThePlanetaryGuy, Associate Professor of Planetary Science at @NCState) says "I'm guessing those white dots are hot pixels" and "it looks like the foreground is an area around 40-ish centimeters (~16 inches) across" and "there are four LEDs as part of the camera system to illuminate the asteroid surface during night-time ops".

  Physically, these “warm/hot pixels” are mainly caused by charge leakages within the image sensor chip.
  Although the warm/hot pixels are randomly distributed within the chip, they are in a fixed position. Under normal
  conditions (shorter exposure times, normal light), many of them are not visible since their contribution to the
  general noise level is below this level.
  pco.knowledge base | warm / hot pixel


texts: What pole is closer to the galactic edge?

texts:
Suppose 2 spaceships leave from the earth's north and South Pole going straight up which one will exit the galaxy first (assume they have the same speed and are going in a totally straight line) ? Edge of the galaxy means absence of stars, this question refers to the up-down edge of this spiral galaxy.
The question is about the current distance from the earths poles to the edge (top/down) not to the galactic plane, as far as I understand after crossing the plane the nearest pole to the edge will be reversed.


texts: Why are explosions always used to represent the Big Bang?

texts: In documentaries the Big Bang is often represented as blackness followed by a big explosion with loud noises. This always feels cheap and falling short of explaining the origin of the Universe. Is this really the best way to get green-thumbs thinking about the origin of the Universe? Are there other, better, representations or analogies of the Big Bang? If so, how do they better describe the current cosmological model than the "explosion" analogy?


texts: How to calculate the heliocentric velocity of an object?

texts: My task is to calculate the heliocentric velocity of an object to correct for wavelength in a spectrum. I have the RA, Dec and observation date, and I know that the  NED velocity correction calculator(https://ned.ipac.caltech.edu/forms/vel_correction.html) will do the job, and I found out the equation here (https://ned.ipac.caltech.edu/help/velc_help.html#notes), but honestly I don't have a clue where these parameters come from. Could some one give me some hints on the reasoning behind it? Thanks!


texts: Is lunar elevation at a given location for a given day unimodal?

texts:
Is lunar elevation at a given location for a given day unimodal:

Unimodal function

In other words, once the moon's elevation reaches a minimum (which may
be above or below the horizon depending on if the moon is
circumpolar), does it increase continuously to its maximum, or can it
decrease briefly and then increase again (resulting in a local minimum
that's not a global minimum) before reaching the maximum.

And also similar to the above as it goes from the maximum elevation
(which may also be above or below the horizon depending on whether the
moon rises at all on a given day).

Why this is important: I think I found a bug in libnova that assumes
the moon is circumpolar if it is above the horizon when it's due
north. This is untrue

My fix
does not assume this, but does assume that lunar elevation is
unimodal.

If that's untrue, I'll need to further fix my fix.

EDIT: Here's how far I've gotten:

The moon's declination and hour angle (at a given location) are
both functions of time. Thus, we can implicitly consider the moon's
declination to be a function of its hour angle. This only works
because the moon never experiences retrograde motion. Bodies that
experience retrograde motion could have two declinations for a given
hour angle, so the declination would no longer be a function of the
hour angle.
Using the standard formula, we see the moon's elevation is:

$$
   \sin ^{-1}(\sin (\text{lat}) \sin (\text{dec}(\text{ha}))+\cos (\text{ha})
    \cos (\text{lat}) \cos (\text{dec}(\text{ha})))
$$

where dec(ha) is the declination at hour angle, ha is the hour angle,
and lat is the latitude.

Since the moon's elevation is a differentiable function (except
potentially at the poles and equator), we find the derivative with
respect to the hour angle:

$$
   \frac{\text{dec}'(\text{ha}) (\sin (\text{lat}) \cos
    (\text{dec}(\text{ha}))-\cos (\text{ha}) \cos (\text{lat}) \sin
    (\text{dec}(\text{ha})))-\sin (\text{ha}) \cos (\text{lat}) \cos
    (\text{dec}(\text{ha}))}{\sqrt{1-(\sin (\text{lat}) \sin
    (\text{dec}(\text{ha}))+\cos (\text{ha}) \cos (\text{lat}) \cos
    (\text{dec}(\text{ha})))^2}}
$$

The moon's elevation will reach a min/max (in the sense of
unimodality) when this derivative is 0. That occurs when:

$
   \sin (\text{ha})\text{ = } \text{dec}'(\text{ha}) (\tan (\text{lat})-\cos
    (\text{ha}) \tan (\text{dec}(\text{ha})))
$

So the question becomes: can this equation have more than two
solutions for 0 < ha < 2*Pi

Which I hope someone answers at: https://math.stackexchange.com/questions/587136/


texts:
How can an extrasolar comet be detected - this is based on an article regarding the influence on a extra solar gas giant on these comets causing changes in their orbit and leading to them being swallowed by the star ..
Still stuck on understanding how we detect them .. they certainly have no measurable effect on the movement of the planet or the star .. and the chemical make-up of the comet seems irrelevant given the size of the star and observations we can make ? Just missing something Simple I think ?


texts: How to calculate the period of a lunar mansion?

texts:
What is the period of a lunar mansion or station referring to and how is it calculated? Wikipedia says the following:

A lunar station, also called a lunar mansion or lunar house, is a segment of the ecliptic through which the Moon passes in its orbit around the Earth. The concept was used by several ancient cultures as part of their calendrical system.

For example, the period days of first lunar station is from April 23rd to May 10th and the period of the last lunar station is the days of April 20th, April 21st and April 22nd.
Please note that the following table is included in the Wikipedia page of Lunar Mansions and also the beginning day of each period is only listed here. For example the duration of the first mansion's period is from April 5th to April 18th. It's from April 18th to May 1st for the second Mansion and so on.


texts: Why isn't the asteroid belt affected by Jupiter's gravitational field?

texts:
Jupiter's mass is just about a 1000th of the sun's and the asteroid belt is slightly closer to Jupiter than it is to the sun.

If the heavier the object, the more curvy space is around it, why isn't the asteroid belt's movement more turbulent owing to the effect of both Jupiter and the sun?


texts: Beta Andromedae (Mirach) and distances mentioned in original Cosmos series from 1980

texts:
In one of the episodes from Carl Sagan's show Cosmos he explains that Beta Andromedae is the second brightest star in the constellation Andromeda, and is 75 light years away. The link to the video is here.

I've looked up this star on Wikipedia and it says it's the brightest star in the constellation, not the second brightest, and instead of 75 light years away it says it's about 197 light years away.

I know that this show Cosmos is quite old. It aired in 1980. I understand our measurements are more accurate nowadays, but I was just wondering if anyone knew why the discrepancy with the brightest and second brightest star claims, and also that the Wikipedia article says it's 197 light years away, a difference of about 260% from the 75 light years mentioned by Sagan. That's quite a significant difference.

His information of the distance from us to the center of our galaxy is quite close: he says 30 thousand light years; Wikipedia says 27 thousand light years. As to our distance to Andromeda, he says: 2 million light years; Wikipedia says 2.5 million light years.

Have I completely got the wrong star that I'm looking up?


texts: Does the mass of the observable universe ever change?

texts:
First do we have anyway to even estimate the mass of the entire observable universe?  And then is there any data that shows mass being gained or lost?  Would we ever know if someone was playing with the til.

Also I want to be clear that I am not talking about small masses on the outskirts of the "universe" or small discrepancies in measurement or anything of the sort.

Note:  I would like to add that maybe we should define the observable universe as NOW (x-date) so that we aren't calculating a moving target.


texts: Are they really sure this isn't an Airy disk? How was that ruled out?

texts:
How do they know that this is a spherical shell of gas, and not just something like an Airy pattern-like artifact produced by the VLT's large interferometric aperture?
Image from: https://www.eso.org/public/images/eso0906b/

I get 180 pixels from center to the first minimum, and 72 pixels = 4 mas. That makes the first minimum at 10 mas or 4.8E-08 radians. The wavelengths are around 1.6 microns so that would correspond to a circular aperture of 40 meters using 1.22 λ/d.
Are they really sure this is a real shell, and not an Airy disk? How was that proven?
From https://www.eso.org/public/news/eso0906/

“We were able to construct an amazing image, and reveal the onion-like structure of the atmosphere of a giant star at a late stage of its life for the first time,” says Antoine Mérand, member of the team. “Numerical models and indirect data have allowed us to imagine the appearance of the star before, but it is quite astounding that we can now see it, and in colour.”
Although it is only 15 by 15 pixel across, the reconstructed image shows an extreme close-up of a star 100 times larger than the Sun, a diameter corresponding roughly to the distance between the Earth and the Sun. This star is, in turn, surrounded by a sphere of molecular gas, which is about three times as large again.
T Leporis, in the constellation of Lepus (the Hare), is located 500 light-years away. It belongs to the family of Mira stars, well known to amateur astronomers. These are giant variable stars that have almost extinguished their nuclear fuel and are losing mass. They are nearing the end of their lives as stars, and will soon die, becoming white dwarfs. The Sun will become a Mira star in a few billion years, engulfing the Earth in the dust and gas expelled in its final throes.
Mira stars are among the biggest factories of molecules and dust in the Universe, and T Leporis is no exception. It pulsates with a period of 380 days and loses the equivalent of the Earth’s mass every year. Since the molecules and dust are formed in the layers of atmosphere surrounding the central star, astronomers would like to be able to see these layers. But this is no easy task, given that the stars themselves are so far away — despite their huge intrinsic size, their apparent radius on the sky can be just half a millionth that of the Sun.
“T Leporis looks so small from the Earth that only an interferometric facility, such as the VLTI at Paranal, can take an image of it. VLTI can resolve stars 15 times smaller than those resolved by the Hubble Space Telescope,” says Le Bouquin.
To create this image with the VLTI astronomers had to observe the star for several consecutive nights, using all the four movable 1.8-metre VLT Auxiliary Telescopes (ATs). The ATs were combined in different groups of three, and were also moved to different positions, creating more new interferometric configurations, so that astronomers could emulate a virtual telescope approximately 100 metres across and build up an image.
“Obtaining images like these was one of the main motivations for building the Very Large Telescope Interferometer. We have now truly entered the era of stellar imaging,” says Mérand.
A perfect illustration of this is another VLTI image showing the double star system Theta1 Orionis C in the Orion Nebula Trapezium. This image, which was the first ever constructed from VLTI data, separates clearly the two young, massive stars from this system. The observations themselves have a spatial resolution of about 2 milli-arcseconds. From these, and several other observations, the team of astronomers, led by Stefan Kraus and Gerd Weigelt from the Max-Planck Institute in Bonn, could derive the properties of the orbit of this binary system, including the total mass of the two stars (47 solar masses) and their distance from us (1350 light-years).


texts: Are there events in universe which we receive first from their neutrino's instead of their photons?

texts:
Neutrino's are very small though they have mass. Because of that it is probably that the don't have a speed faster than photons.

But is it in all events, like supernova's or else events, where it is possible that we first receive their neutrino's instead of their light?

Perhaps gravity or other interactions could change something in their way to earth?


texts: What happens if gravity shuts down for only one second?

texts: What would happen if gravity completely stopped for 1 second?


texts: Would humans hear gravity waves from a binary BH fusion nearby?

texts:
The frequency of the gravity waves detected by aLIGO recently were in the audible sound spectra. Actually spanning over half of the keys of a piano, I've been told, during 2/10 or so seconds.

Would a human ear sense a gravity wave if powerful enough? The waves going through empty space from the event horizons, through the walls of a spacecraft and through the ears of astronauts. Would one actually hear a "zip" sound because space makes waves inside our ears?


texts: Will stars live longer if they consume more hydrogen?

texts: I heard that stars would live longer if they consumed more hydrogen and material from their 'environment'. Is that true? For example, if the sun consumed all of the gas giants, would it live a little bit longer?


texts: What is the brightest star (relative magnitude) in M31?

texts: I am wondering what the brightest individual star is in M31, the Andromeda Galaxy.  Specifically, brightest as seen from Earth (so relative magnitude).


texts: Does the radio signal decay when it travels through the intergalactic space?

texts: When you emit the radio signal it starts moving at the speed of light. Radio beam is diffusing with each kilometer the signal has traveled. To the nearby receiver the signal is strong. But if the receiver is far away, the signal will become weaker and weaker until it becomes a noise. So the question is does the same happen in deep space and what distance radio signal (or any electromagnetic wave frequency) could travel until it becomes noise?


texts: How can I observe Sgr A* with itelescope.net

texts:
I've been experimenting with itelescope.net and tried to observe Sgr A*.

I was wondering if there are any suggestions how I can best observe the surrounding stars.


texts: Is there, in fact, any close-up photography of Saturn's rings, showing individual pebbles/rocks?

texts:
After reading this excellent but difficult answer, https://astronomy.stackexchange.com/a/18407/13071

I've been thinking how difficult it is to get a sense of the distance between and the size of typical items of dust, pebbles, rocks and/or anything else in Saturn's rings.

In short, have any photographs been taken by spacecraft, more or less "in" the rings, close enough to actually see individual dust, pebbles and/or rocks?

(As I understand it, the rings are on the order of 10m thick.  So I'm asking, have any photos been taken from that order of distance from the rings?  What's simply the closest viewpoint ever taken?)

Failing that, is there perhaps an artist's rendition somewhere of "what you'd see from 100m above the rings looking straight down at them?"  What would be in that frustrum - nothing?  Lots of fist-size rocks you could see? Or?

It's completely unclear to me if each (say) pebble-size piece is inches apart, meters apart, or for all I know 100s of km apart?


texts: make a celestial map from deep sky images

texts:
I take pictures of deep sky objects and I would like to make a celestial map that contains the pictures in the right position in the sky.
Ideally something like stellarium. (but in stellarium it's hard and you have generated stars on top of the pictures).
it would be nice to have automatic plate solving, but otherwise I can try to use an external plate solver and provide to software/library directly the fits file. The method should accept colored images, I see many software that handle only gray fits files.
In other words a 3D black sphere where the pictures are automatically positioned, and the possibility to render a part of the 3D map or the entire map, or navigate like in stellarium.
I prefer linux software or python3 scripts/libraries.
Thanks!


texts: If there is no matter inside any of the black holes and all of them have a singularity in the center of them, which is infinitely small and infinitely dense, then how can they differ in size and weight?


texts: Why there are three equations governing blackbody emission?

texts:
I learnt that the spectrum of a black body can be explained using

Planck distribution
Rayleigh -Jeans equation and
Weins displacement law

Can anyone tell me why there are three different equations that explain the same physical phenomena and when should I consider which equation?


texts: How to calculate solar coordinates. (Right Ascension, Declination, and ultimately the Altitude and Azimuth of the Sun)

texts:
As the title says I am trying to calculate solar coordinates of the sun for a given location and time. I have spent many 10's of hours on this without success so I will sincerely appreciate help on this.  My RA value seems to be right on but the Dec, Alt and Az are off.

Alt value is within 6 degrees but I cannot figure out why it is that close because the latitude is in radians instead of degrees like the other values. If I change latitude to degrees the values don't even make sense.

I have included all the values of the intermediate variables to help see at a glance what might be off. I hard coded the JD and the Local Hour Angle just to take those out of the equation for debugging.  Links are shown as to where I got those values.

The C# code is below although the programming language doesn't matter. The formulas are the same in any language.

  //for formulas
            double D = 2458599.125000 - 2451545.0; //the  first  term is the jd of interest; 2nd term is jd of 1-1-2000 at 12:00:00.0
            double Latitude = 41.369341;
            double Longitude = 81.885493;

            double gTmp = 357.529 + 0.98560028 * D;  //mean anomaly of the sun  = 7310.0765751550007
            double gTmp1 = (gTmp % 360);     //subtract multiples of 360 (returns remainder in degrees)  =  110.07657515500068
            double g = gTmp1 * Math.PI / 180;   //Convert to radians = 1.9211986657737494
            double qTmp = 280.459 + 0.98564736 * D; //mean longitude of the sun = 7233.33868336
            double qTmp1 = (qTmp % 360); //subtract multiples of 360 (returns remainder in degrees) =  33.338683359999777
            double q = qTmp1;   //don't convert to radians here; convert after terms in degrees are added in the computation of L; =33.338683359999777
            double L_tmp = q + 1.915 * Math.Sin(g) + 0.020 * Math.Sin(2 * g);//geocentric apparent ecliptic longitude of the sun(adjusted for aberration) = 35.124421105295383
            var L = (L_tmp % 360) * Math.PI / 180;   //Convert to radians; //subtract multiples of 360 = 0.61303679614439033
            double eTmp = 23.4393 - 0.00000036 * D;  // = 23.436760515
            double e = eTmp * Math.PI / 180;   //Convert to radians;   = 0.40904863698815186

            //http://www.neoprogrammics.com/de405_usno_ae98/DE405_Sun.php
            // formulas per https://aa.usno.navy.mil/faq/docs/SunApprox.php
            double RA = (Math.Atan2(Math.Cos(e) * Math.Sin(L), Math.Cos(L))) * 180 / Math.PI; //right ascension converted from radians to degrees = 32.838762087228496
            double dec = (Math.Asin(Math.Sin(e) * Math.Sin(L))) * 180 / Math.PI;  //declination converted from radians to degrees =  3.228747909189217
            string[] sunCoordinates = new string[2];
            sunCoordinates[0] = ToHMSStr(RA);    // = "2h 11m 21.3s"
            sunCoordinates[1] = ToDMSstr(dec);  //  = "13d 13m 43.49s"

            //compute alt and az per https://aa.usno.navy.mil/faq/docs/Alt_Az.php and https://aa.usno.navy.mil/faq/docs/GAST.php
            //LHA for testing is from https://ssd.jpl.nasa.gov/horizons.cgi#results and https://www.vercalendario.info/en/how/convert-ra-degrees-hours.html
            //from http://www.neoprogrammics.com/de405_usno_ae98/DE405_Sun.php
            double LHA = 307.39;   //Local Hour Angle
            double lat = Latitude * Math.PI / 180; //Convert to radians; //Latitude is defined above; We get sign (below) after converted to Rad????  = 0.72203120983028346
            double alt = (Math.Cos(LHA) * Math.Cos(dec) * Math.Cos(lat) + Math.Sin(dec) * Math.Sin(lat)) * 180 / Math.PI; //convert from radians  = 53.266598643452909
            double az =Math.Atan2(-Math.Sin(LHA) * Math.PI / 180, (Math.Tan(dec)*Math.Cos(lat) * Math.PI / 180 - Math.Sin(lat) * Math.Cos(LHA)) * Math.PI / 180); //convert each term to radians   = 2.4585704411338072
            az = az * 180 / Math.PI;   //convert from radians   = 140.86570991258415

```


texts: What are the stars/constellations a beginner/enthusiast can easily identify?

texts:
I was just wondering what are some of the stars, constellations or any other things that one can just identify by looking up at the night sky.

For example, when ever i look up, I immediately see Orion and can identify Betelgeuse, Rigel, Bellatrix. Apart from that i can identify some of the bright stars liike sirius , vega.
So, what other stars are there that one can easily identify and point?


texts: What is the density of the solar system per cubic light second outside the Jupiter ecliptic?

texts:
It would seem logical that there is some amount of material falling from the Oort cloud toward the Sun and other mass concentrations in the Jupiter Ecliptic disc defined by Jupiter's gravitational field.
Is there any research to determine the distribution of this material related to the the Massive objects in the the system ?


texts: Can mechanical angular momentum be transferred by gravity?

texts:
At PSE there are a few answers that explain that since the moon is responsible for tides and tides slow down spinning, L must be transferred to the moon.

This implies that if earth's L were reduced by an asteroid, this would not influence the moon's orbit.

Can you  clarify:

does the change of $\omega$ of the Earth alter the orbit of moon only when that change is attributable to the moon or in any case?
would there be tides if there were no moon?
what is the mechanism through which angular momenta can exchange magnitude? This is apparently impossible since there is no connection or, we we consider the obsolete Netwonian gravity, the connection is radial and never tangential?


texts: Catching up with Hubble domain galaxy at constant acceleration: is it possible? If yes, what time will it be when I arrive?

texts:
An elf gave me a magic spaceship for Christmas: it can maintain a thrust of $\alpha = 10\ \mathrm{N/kg}$ indefinitely. Otherwise, I'm still constrained by physics. I plan to set out on a journey into space at constant acceleration in a straight line from Earth.

Far away galaxies recede from Earth at a velocity $v$ proportional to their distance $x$ (Hubble's law):
$$v=Hx,$$
where $H$ is the Hubble parameter, currently about 67.8 (km/s)/Mpc.

Question 1: While I accelerate, can I eventually match velocity with a galaxy at the same distance from Earth as myself? So I could effectively catch up to a galaxy by cutting down the thrust at the right moment and thus get in orbit around a planet without braking too hard?

I have been able to make a naïve calculation based on special relativity as follows, but as some comments suggest, an actual answer should also include a discussion of general relativistic effects, especially where they cannot be neglected.

Here is my naïve calculation: when I start my journey, I first crawl slowly out of Earth's gravity well for a short time, maybe for a day or so, by which I reach a domain where gravity is small compared to my thrust. I'm then in a domain governed by special relativity, where my distance from Earth is governed by hyperbolic motion
$$x=\frac{c^2}{\alpha}\left(\cosh\frac{\alpha\tau}{c}-1\right),$$
where $\tau$ is the proper time as measured on my spaceship (in particular, $x$ and $\tau$ are measured in different frames of reference).

After one year of travel, I'm a bit over half a light-year away from Earth, and the Sun is still the closest star in the sky. After ten years, I'm about 17000 ly away, with the disk of the milky way behind me. After 17-18 years, I'm roughly 10 Mpc out, where Hubble's law starts becoming valid. My velocity relative to Earth is
$$v=c\tanh\frac{\alpha\tau}{c}.$$
Plugging $x$ and $v$ into Hubble's law above yields
$$\tanh\frac{\alpha\tau}{c}=\frac{Hc}{\alpha}\left(\cosh\frac{\alpha\tau}{c}-1\right).$$
For large values of $\alpha\tau/c$, $\tanh\approx 1$ and $\cosh\approx\exp/2$. With the elf's choice of $\alpha$, a large value would be $\tau\gg 1\ \mathrm{year}$. We need to assume $\tau > 17\ \mathrm{a}$ anyway, and solving for $\tau$ yields
$$\tau\approx\frac{c}{\alpha}\ln\left(2+\frac{2\alpha}{Hc}\right)\approx 42\ \mathrm{years}.$$
The possible problem I see with this calculation is that while on the spaceship, only 42 years pass, a much longer time will have passed on Earth, possibly leading to changes in the Universe/Hubble parameter to break the calculation.

Now, if it is possible to find a nearby galaxy at velocity zero relative to the spaceship after half a human lifetime, I could find myself a nice Earth-like planet and chat with the folks there.

Question 2: What time would it be on the planet? I don't mean teatime, but more like, what would their answer be if I asked, how long since the Big Bang? Would it be similar to the answer I'd get on Earth (13.7 Ga)? After all, I travelled for only 42 years without changing direction, experiencing Earth-like acceleration all the way.


texts: Are there recent estimates of Kuiper belt mass?

texts:
What is the mass of the Kuiper belt? Obviously estimates will be highly uncertain, but for my application I would like to find a decent current estimate.

The papers I found so far: (Gladman et al. 2001) estimates it to 0.1 Earth-masses, (Trujillo, Lewitt & Luu 2001) gets the mass of bodies between 100 km and 2000 km to 0.03 Earth-masses, (Kenyon & Bromley 2004) estimate on the order of 0.5 Earth-masses (assuming a starting mass of 10 and then losing 95%), (Fraser et al 2014) estimate just $\sim$0.01 Earth-masses.

These papers are a bit old, and I suspect there have been more recent observations improving on the estimates. There is a fair number of papers discussing how to resolve this discrepancy between disk models predicting 10-30 Earth-masses and these low numbers, but I am more interested in empirical estimates.

So, what is the current consensus on the Kuiper belt mass and its uncertainty?


texts: Why the Hubble constant is so inconsistent?

texts:
Having a look on Wikipedia I noticed the following values (of the last 6 years) for the Hubble constant:

67.6±0.7 SDSS-III Baryon Oscillation Spectroscopic Survey
73.00±1.75   Hubble Space Telescope
67.80±0.77   Planck Mission
69.32±0.80   WMAP (9-years)
70.4±1.3     WMAP (7-years)

Most of experiments exclude the values of the others so that WMAP excludes the values of SDSS and from Hubble, while Hubble excludes Plank Mission's values, SDSS and WMAP 9.
Can anybody tell what's the problem here and which one is the more reliable source for $H_0$?


texts: Can the Earth be used as a gravitational lens?

texts: Could the Earth be used as a gravitational lens to image very far distances with an effective aperture that would be far greater than any telescope? How far away from Earth would an observing spacecraft have to get to enter the focal point, and see very far at a resolution? Would that enable the direct imaging of small planets around other stars?


texts: Need advice on mirror-making for a home-made amateur reflector

texts: For example, what would be some good references to read first? What sort of glass slab should I use? What size; diameter and thickness. Im a first-time builder trying to build one


texts:
There are red stars, and orange stars, and yellow stars, and blue stars, and they are all understandable save the fact that there is a 'gap': There are no green stars.

Is this because of hydrogen's chemical properties (e.g. the emission spectrum) or some other reason? Or are there just green stars that I have no idea of? If so, I need some pictures; they must look awesome.


texts: Distance between each dish in an array telescope configuration

texts: In an array telescope configuration, like VLA and ATA, what dictates the distance between each dish?


texts: Early (high density) Universe's event horizon

texts:
Taking into consideration the big bang theory and the followed expansion of our Universe, was there a time when density of the Universe created an event horizon?
If so, then for how long and how is it that it kept expanding despite such an enormous density and space-time deformation?
I did a very brief estimation for only barionic and dark matter taking into account that there are about 1e11 estimated galaxies in observable Universe and there are about 1e11 stars per galaxy (red dwarfs are most common, but I used the Sun's mass) and that the dark matter equals about 4 time barionic matter - the online calculator showed an event horizon as ~1e11 ly.
Was this result in the right ballpark and what does it imply if so?
PS. I've seen similar questions here, so pointing to some articles will be fine, explaining consequences will be even better
PS. My question does not seem to be answered by the one mentioned in the closing comment, as suggested to me I edit to reopen it.
Edit (3/25)
As far as I understood the "duplicate" question is about potential event horizon if the Universe's density was at a point, i.e. if the Universe was a black hole, which it obviously is not (as I read somewhere), my question was that some time in the past the Universe had to be dense enough to be one, if not why not, if yes, why it kept expanding and what happened to the event horizon.
I see it as either eternal inflation is the case and there has never been a singularity or the early Universe had something black holes do not, which made it to keep expanding, or simply just the fact that space-time arose from the singularity it has never been a black hole.
Just wanted to ask what the current theories (especially GR) can say about it.
thanks


texts: The moon has just the right speed not to crash on the Earth or escape into space. What are the odds?

texts:
My understanding is that the moon was created a long time ago when Earth was hit by a big asteroid.
The debris then agglomerated into the Moon, which happens to be orbiting at the exact speed required to neither crash back into the Earth, nor escape into space.
Having the exact correct speed seems extremely unlikely. Yet, our moon is there, and many other planets have moons.
Are these just the few survivors out of thousands of events that didnt have the « goldilock » speed?


texts:
Are Trans-Neptunian Objects (TNOs) asteroids?

Please, base your answer. If possible, give sources. Thanks.


texts:
I will expect that gravitational lensing should turn an object into a ring image. But I saw in some situations that instead multiple images are formed. For example, the Einstein-cross in the image below, consisting of four images:

Why is it so?


texts: Asteroid locations at the time of the crucifixion of Jesus

texts:
I am interested in learning the locations and velocities of the near earth asteroids at the time of the crucifixion of Jesus Christ.
 I would like to back-calculate the paths of all known near earth asteroids to find out if any was between the earth and the sun at the time of Jesus' crucifixion on Good Friday.  The Horizons system of NASA JPL only permits back calculations to about 1400AD.

I want to see if there was a clustering of asteroids on Good Friday between the earth and sun.  If so they could be the remnants of a gigantic collision that would have been capable of making a dust cloud in interplanetary space that could have produced a shadow on the entire earth which would account for the observations reported by the gospels and the Chinese astronomers and St. Dionysius and others.

In other words if any asteroids are calculated to have been between the earth and sun on Good Friday they may be left-over debris from the possible collision that produced the dust cloud.

My question is this.  Do you know of any available computer program like the JPL  Horizons program that will work to give asteroid positions back in the time period between 29AD and 35AD?  (I give a range of years because biblical scholars give a range of possible years for the Crucifixion of Jesus.  The determination of a debris asteroid would help historians know the timing of the Crucifixion better, also.)
Thank you for your attention and assistance.
Best Regards,
Dr. Francis Kelly
President, The Catholic Association of Scientists and Engineers


texts: Where can I find the image of MY Camelopardalis?

texts:
In this news article, it says

  The image captured by the telescope at the Calar Alto Observatory in southern Spain, reveal the physical properties of each of the stars including temperature and shape.

I Googled to see the actual image but unfortunately all are graphical images.So can I see the actual image as captured by the Calar Alto Observatory?


texts:
Not sure if this is the right StackExchange for this, but seems appropriate.

Is there any off-the-shelf software that can display a star field (view of the night sky) as if seen from a particular location and looking in a particular direction?  Ideally, I'd like to be able to specify the location (Lat/Lon coordinates) and the direction in which the virtual camera is pointing, and get an image of the starfield.

The ability to modify the parameters of the virtual camera would be of additional benefit.

Free software would be best, but paid may be ok as well, depending on the price.


texts: When will the next series of mutual eclipses of Jupiter's moons begin?

texts:
When I was young (I won't tell you when) I saw one of the four Galilean moons of Jupiter suddenly disappear while watching through a small refractor. It wasn't a coincidence, I'd seen the prediction in some announcements in Sky and Telescope and it happened like clockwork. The orbital plane of the Galilean moons had rotated so that it included the Sun, and the moons were Eclipsing each other, or so I remember.

Will this happen again? If so, when will they start, and where can I find predictions of individual eclipses?


texts: How did DSCOVR capture the Moon's shadow on Earth during the August 21 2017 solar eclipse without the Moon itself also being visible?

texts:
In this gif you can clearly see the Moon's shadow moving from the West Coast of the U.S. towards the East Coast during the August 21 2017 eclipse.
DSCOVR (the satellite that imaged this) is located at the L1 point, which is exactly between the Earth and the Sun, meaning it always sees the sun-lit part of Earth.
But for a Solar eclipse to happen, the Moon also has to be exactly between the Earth and the Sun, and thus it should be visible in this gif.
At first I thought it was because DSCOVR was closer to Earth than the Moon was, but it's actually more than 3 times farther away.
Geometry dictates the Moon should be between the Earth and DSCOVR since DSCOVR itself is between the Earth and the Sun, so why isn't the Moon visible?


texts: Difference between luminosity, luminous flux, and radiant flux?

texts: I've looked this up, and was wondering the differences between them. Luminosity is the total energy emitted by a source, in watts. However, I'm confused about luminous flux and radiant flux. Since radiant flux is the total energy emitted by an object, would that make luminosity the same as radiant flux? Then how does luminous flux relate to luminosity? Is luminous flux just radiant flux, but only showing the visible light? And this website, https://www.ifa.hawaii.edu/~barnes/ASTR110L_S03/inversesquare.html, says lumens are a unit of luminosity, but how if lumens are candela times steradians?


texts:
In preperation for the upcoming solar eclipse I'd like to practice my photography to be able to take some (hopefully) good photos of the corona during totallity.

What is the brightness of the sun's corona? How bright is it compared to a full moon (or other celestial phenomena)?

At what point during the "diamond ring" does it become too bright to look at safely without safety equipment, and what is the relative brightness of the diamond?


texts: Estimating the virial mass of a galaxy cluster from its $M_{500}$ measurement

texts: In this paper, the authors seem to calculate the virial mass of the Fornax cluster by using its $M_{500}$ value. In the section 4.1, they say its mass was measured to be $M_{500}=6.4\times 10^{13} h^{-1}M_\odot$ and then adds that the corresponding virial mass is $M_{\text{vir}}=1.2\times 10^{14}h^{-1}M_{\odot} $. I don't understand how such a calculation is possible. Could someone please explain how it is done?


texts: Is the Dwarf Planet class really necessary?

texts:
Another way of asking this is, what is the difference between dwarf planets and asteroids? Aren't they the same things? It's just that some asteroids are spherical and others aren't...or is there something else?

I can understand why Pluto was demoted. Same thing happened to Ceres (after 50 years of being called a planet?) when we found out it was in an asteroid belt. It would be more helpful to laymen, I think, if the Kuiper Belt was renamed to the Second Asteroid Belt or maybe the Icy Asteroid Belt.

But why not stick to the original classes where we only had planet and asteroid? (and moon i guess.) Why add a new class called dwarf planets? Was it just to temper the protests?

EDIT: I forgot to add, we never needed a dwarf planet class before, despite knowing that Ceres was spherical for a long time. So where has this need, if it really exists, come from?


texts: If thousands of exoplanets have been discovered, why haven't we discovered planet 9 yet?

texts: According to NASA, we've discovered 3,453 exoplanets so far [1]. With some of the farthest being at 13,000 light years away [2]. This would suggest today scientists have a really advanced capability for this kind of discoveries. However, the existence of a ninth planet in the solar system (which has not only been proposed but its characteristics are already predicted with great precision[3]) has not yet been discovered. If a ninth planet existed in our solar system, shouldn't it have already been discovered? How can exoplanets thousands of light years away be discovered weekly, while a giant planet right in our backyard still lays undiscovered?


texts: How scientists estimated the number of near-Earth supernovae over the last 11 million years?

texts:
According to this article on wikipedia,

  An estimated 20 supernova explosions have happened within 300 pc of
  the Earth over the last 11 million years.

How did scientists determine that 20 near-Earth supernovae were within 300 pc over the last 11 million years? If this was empirically observed, then how do we know that there are not more supernovae that we haven't seen? If this estimate is obtained by some model, then what is the model and why do we trust this model - have there been enough observed supernova to trust that the accuracy of this model?

The source for the statement quoted above is cited here. I skimmed through the introduction and conclusion section of the article. It appears to me that the authors of this paper use the geologic record of radioactive elements to determine this "magic" number of 20. To my understanding, if one knows the initial/final concentration of a radioactive isotope, the decay rate of said isotope, and the time-interval to be considered, then one can deduce the final/initial concentration. Using this logic, how was the initial concentration tied exclusively to supernova (as opposed to a combination of things)? I am inclined to think that no other mechanism exists that can produce these isotopes over these time-frames, but even if this is the case - why?  I don't know if this is correct, and would like to know more about this topic. If I double the time-interval from 11 million years to 22 million years, would the estimated number of near-Earth supernova also increase by a proportional amount (maybe double 20 --> 40, or by a factor of 2 * r^2 assuming spherical distribution), or would the "within 300 pc" metric change this number due to the acceleration expansion of the universe?


texts:
I want to build a Machine Learning model to approximate effective temperatures of stars based on their B-V index but there aren't that many catalogues that include that. I came across the Vizier catalogue (http://vizier.u-strasbg.fr/viz-bin/VizieR-3?-source=V/19/data) and I wanted to be sure if that's a catalogue for individual stars that I can leverage.

Or, do you know what other resources could help in that regard? Or suggestions?

Thanks


texts: Does anyone know why three of Jupiter's largest moons orbit in 1:2:4 resonance?

texts:
Three of the first four moons ever discovered outside of our own planetary sphere of gravitational influence orbit in very close to perfect resonance. Europa's orbit is almost exactly twice as long as Io's, and Ganymede's is almost exactly twice as long as Europa's. Perhaps it is just coincidence. If you look at enough random things, you start to see patterns that aren't necessarily there. But it would be a pretty big coincidence. When I see something like this in nature, I have to wonder if there is an underlying cause.

The ratios aren't quite exactly 2, so if there is a gravitational influence or something that pulls them into this resonance, the influence must not be overpowering enough to force exact resonance. Or maybe it is, given enough time, but "recent" collisions or the pull of other satellites in the system may have driven them a little bit off of their resonance. Has anyone studied this and found a probable reason for this phenomenon?


texts: Is there any formulae to calculate whether the sun will depress 18 degrees or more below the horizon on a certain day / location?

texts:
I'm trying to code a piece of software which will calculate some times for me that would greatly help me in my day to day but none of my formulae work if the sun doesn't go at least 18 degrees below the horizon.

In this case, I have different formulae to use but I need to program the software to be able to use this other formula on these days. I have no way of determining the maximum the sun will depress below the horizon on any specific day or location.

I am not an expert in any sense of the word in astronomy and literally only know what is relevant to what I need, but I think what I am trying to ask is if it is possible to determine the if the minimum solar elevation / altitude angle is less than -18 degrees on a day / location.

I have attempted to search but was unsuccessful and am even unsure if what I am asking for is even possible.

Thanks for any help!


texts: Determining the shape of ʻOumuamua via stellar occultation

texts:
As far as I know, our current knowledge regarding the exact shape and size of ʻOumuamua is based on the analysis of its light curve and the assumption that it has a uniform albedo.

ʻOumuamua is very dark and too small to be resolved by even the largest telescopes as much more than a point of light. But so is Ultima Thule and we did manage to get a really good idea of its size and shape by observing stellar occultations caused by it.

Could the same technique be used to get a better idea of what shape ʻOumuamua really is? Or does its hyperbolic orbit render this kind of observation impractical? Have any attempts been made to perform such observations?


texts: Bounded Observable Universe; is there an object we once could see but can no longer?

texts:
If the universe is expanding faster than the speed of light, then there will be objects (matter or energy or whatever) that previously could be seen, but no longer can be seen, precisely because the universe is expanding faster than the speed of light.

Is there such an object that we can no longer see, though previously we could see it?


texts: The nature of cosmological inflation — unfolding dimensions?

texts:
While the paradigm of cosmological inflation is well established, the nature of the inflation is not known and is tackled by introduction of a hypothetical "inflaton" field.

I was wondering if there are theories or research exploring the idea that after the Big Bang the Universe had just one spatial dimension at first and therefore quite different expansion dynamics (compared to expansion along all dimensions at once), which may eliminate the need for the inflaton field. And as this simple Universe grew in size and complexity it gained the additional dimensions that slowed down the rate of expansion.

In terms of String theory this would probably mean that spatial dimensions were "rolled-up" initially and "unfolded" in stages with time after the Big Bang.


texts: How could original astronomers have used the clouds to find distances?

texts: I was looking at a very bright moon tonight through light cloud cover and saw a halo of light far bigger than the moon imposed on the clouds. Almost in a conic shape by comparison. I was wondering if early astronomers could use this difference to calculate the distance of the moon given the height of the cloud and the dimensions of earth.


texts:
I understand that there are magnificent tidal forces that come with getting too close to Jupiter, but what is causing comets like Shoemaker-Levy to get torn apart?

I wouldn't expect that the gravitational forces are so strong that spaghetification occurs, is it?


texts:
https://www.nasa.gov/multimedia/imagegallery/image_feature_476.html
Please notice especially the bright star at the center of the image, and how the most massive stars have etched out a cavity in the HI and molecular cloud. It is noticeable that the star near the center that has a number of stars seemingly radiating from it.

What kind of process could create such stellar radiating structures, if real?
Is the spacing related to the Jeans radius?  Thank you.


texts: Is star a necessary phase in black hole lifecycle?

texts: It now seems general fact that when a massive star core collapses at the end of its lifecycle it forms a black hole, can a black hole be formed skipping the star phase altogether?


texts:
This nice page from NASA has the possibility to create an astronomical events calendar for a certain period. I tried to do that for the year 2017 for Central Europe. What comes out puzzles me:

On July 8th the Moon is at it's south Declination. On July 12th the Moon goes through the descending node. On July 22nd it finds itself at the north Declination.

I had always though the south Declination means the southernmost point of the Moon on its orbit. Furthermore I had always thought the descending node is the point the Moon passes by going "down" in its motion. How can it reach a southernmost point and later go even further downwards?
I had been inclined to think that the north and south Declinations would be about half way between nodes (give or take due to slight changes during the motion). How can the Moon be in one of these south or north points and only 4 days later pass a node? And take again 9 more days to reach a south/north Declination again?

It would be nice if the answer could, besides clarifying these concepts (ascending and descending node, south and north Declination), point me to a reading where they as well as other Moon orbital points and parameters are clearly defined and explained.


texts: How to calculate conjunctions of 2 planets

texts:
So, the recent conjunction of Jupiter and Venus seems to have spawned lots of excitement over this "rare" event. But what I can't figure out, is exactly how rare it is. And I've seen such conflicting claims and calculations that I figured I'd better calculate it myself. The only problem is I'm no astronomer. So, does anyone know of a program that can calculate all the conjunctions between a date range that are within a degree of each other? Or does smart person know how to calculate it manually? :)
    I have a program called Stellerium which I've been using to view the various conjunctions that people have mentioned. I don't know if I can use it in the way I need it though. Any help? :)
Thanks


texts:
I was reading an article by David O'Brien et al. where it stated

  "in meteorites only the water bound to the silicates can be found, all the water ice having been lost, whereas on asteroids water ice itself has been detected"

  https://www.sciencedirect.com/science/article/pii/S0019103514002620

Now this was published in 2014, so I'm wondering what is the validity of this statement today. Have we, since the publication of this article, discovered water ice on meteorites?


texts:
I’ve written a script based on Meeus’s Astronomical Algorithms to calculate the position of the sun, moon etc. up to about 4000 BC.
Everything looks good, except when I go to 4000 BC the solstice are about a month after expected dates (they fall mid-July and mid-January.
I checked through this forum and came across this: https://astronomy.stackexchange.com/a/13009 . I looked at the results and saw that we have very similar dates.

Does the precession mean the solstices and equinoxes can shift to this extent? Or have I forgotten a step?

Many thanks.


texts: Are there equations to simulate creation of a solar system?

texts:
I've been wanting to create a simulator to run tests based on properties of a star to find patterns in how planets form. Are there any already made equations for any of these countless relationships? Here are a few examples to further explain what sort of information I am looking for.

For example, how does the mass of a star relate to the distance of the frost line, and is there an already existing equation to estimate this?

More general example; If I wanted to find out how to estimate, say, a planets surface temperature based on a stars temperature and distance, what is the best way to do this?

Another example; To find the most likely average mass of a potential planet, what information would I need? Distance to star? Stars mass? Distance to nearest planets?

Another; How would I go about finding likely measurements of compositions of any hypothetical planets (surface/atmosphere/etc)

Absolutely any information is very welcome. I do not require any form of proven or precise measurements. If there is no equations, then all I need is what factors are involved in specific attribute development.

I'd like to emphasize my understanding that this is an extremely complex subject to go into detail. All I am asking for is any information or recommendations.

Here is a related question to my dilemma, in addition to this information, I am looking for more. Absolutely anything that may help, probably will. I am attempting to make as highly detailed of a model as possible.


texts: Will the UK be able to witness the tetrad in April 2014?

texts: I live in the UK and am aged 15. I have become extremely interested in astronomy, astrophysics, the lot. Basically I have never seen a tetrad and believe this will be my first time - at least understanding what it is. I'm hoping it will be possible and if so where will it be seen in the sky? As in North, South etc. Thanks!


texts: Why doesn't sunrise shift as we revolve around the sun (ignoring seasonal variations - so at the equator)

texts:
If the Earth rotates at a constant speed why doesn't sunrise change as we orbit the Sun?
For example if viewing the Earth's orbit from above at time N let's assume the Earth is at the 3 'o' clock position and so the point on the Earth's surface at the equator perpendicular to the Sun would be in daylight (~12pm local time) let's call this point X (would be at the Earth's 9 'o' clock position).
Six months later the Earth would be at the 9 'o' clock position in its' orbit and assuming the Earth has completed exactly 182 full rotations that point X will again be at the Earth's 9 'o' clock position but would now be facing away from the sun therefore it would be dark but exactly 182 days have passed so it should be (~12pm local time).
I'm probably overlooking something obvious but hoping someone can explain why this obviously isn't what happens in reality.
Many thanks.


texts: How can I calculate solar intensity at Saturn

texts: I'm trying to work out how big solar panels have to be for a Saturn probe, but can't find any data for solar energy at Saturn.


texts: Determination of High-Accuracy Distances of Terrestrial Planets from the Sun

texts:
I understand how in olden days the Sun-Planet distances were estimated using:-
(i) measures of planet orbital periods ($T$) from analysis of observations over several centuries;
(ii) Kepler's 3rd Law $(T^2 = k.a^3)$ applied to the planet orbital periods to determine the relative lengths of the Sun-Planet semi-major axis distances ($a$) expressed in terms of the AU (astronomical unit = distance from centre of Earth to centre of Sun);
(iii) particular Earth-Planet distances along Solar radials were measured using Parallax techniques such as that by Casinni for Mars and Transits of Venus;
(iv) From one or more Earth-Planet radial distances the length of the AU could then be determined by simple algebra.
(v) Other Sun-Planet distances could then be determined once the AU length was found.
Modern ephemerides e.g. those issued by JPL use various techniques:-

The orbits of the inner planets are known to subkilometer accuracy through fitting radio tracking measurements of spacecraft in orbit about them. Very long baseline interferometry measurements of spacecraft at Mars allow the orientation of the ephemeris to be tied to the International Celestial Reference Frame with an accuracy of 0′′.0002. This orientation is the limiting error source for the orbits of the terrestrial planets, and corresponds to orbit uncertainties of a few hundred meters.
The orbits of Jupiter and Saturn are determined to accuracies of tens of kilometers as a result of fitting spacecraft tracking data.
The orbits of Uranus, Neptune, and Pluto are determined primarily from astrometric observations, for which measurement uncertainties due to the Earth’s atmosphere, combined with star catalog uncertainties, limit position accuracies to several thousand kilometers.

from Folkner et al 2014.
I understand how spaceraft telemetry has been used to obtain highly accurate distances between Earth and the terrestrial planets.  But I am not clear about how highly-accurate distances can be determined between those planets and the centre of the Sun.
Question
Do such (Sun-planet-distance) determinations still basically rely on (the more accurate Newtonian version of) Kepler's 3rd Law relating planet orbital period and Sun-planet semi-major axis distance?
$$\frac{T^2}{a^3} = \frac{4 \pi^2}{G(M+m)}$$
What other methods or assumptions are used/involved?
EDIT - Afterthoughts
After further thought prompted by feedback from  u/atmosphericprisonescape
my question boils down to  "How are the positions (over time) of the Sun's Centre tied-in (with sub-kilometre accuracy) to the 4D space-time array of triangulated, high-accuracy, telemetry-derived, Terrestrial planet position determinations.
I guess that Kepler's 3rd Law is not invoked as such. Rather, high-accuracy (sub-kilometre) determinations of the position of the Solar centre presumably require (in addition to the high-accuracy planet positions) some specific deterministic "motivation model"; i.e. a model of motion-determining factors.
These factors would include Newtonian Inertia, Newtonian Gravitational forces and Non-Newtonian factors leading to additional orbital angular velocity (cf Non-Newtonian Perihelion Precession and General Relativity as described at  wikipedia/Apsidal_precession ).
The "motivation model" would constrain the relative positions of the Sun and planets via their involment as motion generators, reactors and enactors.


texts:
I am considering using a 50mm f1.8 maybe even try aN 85mm f1.8 on my Astro FI 102MM Telescope have you any thoughts or suggestions?
I have never taken images via a telescope so this is a whole new learning curve. Need to get my brain back in gear, stopped shooting over 5yrs ago due to the gear being too heavy and my back injury not coping so this will be a much easier way of holding the camera...I HOPE.


texts: Some say that a black hole is a rip in space-time, a portal linking two points in the universe as one. How sound is this? I've read that when a giant star collapses, what is left behind (a massive neutron star?) is so dense that light cannot even escape its gravitational pull. Is this phenomenon caused by an actual object? If one were to travel into a black hole, should not one find only really dense matter?


texts:
The new Google Maps1 presents an actual view of Earth, with the current position of Sun illuminating half part of Earth in real time. It is quite an exquisite view.

My question is based on the following image:

As you can see, Sun's reflection from southern Atlantic Ocean looks very charming. But does it really happen like that? If we travel far2 from Earth, can we actually see Sun's reflection or it is just something Google added for aesthetics?

1: Yes, I don't like most of its new features too, especially when they broke several of the old ones. But that's a separate discussion.

2: Although, the camera's supposed position would be close to geostationary orbit, I guess the reflection can also been seen as close as ISS or Hubble.


texts: What kind of reddish wood is it exactly that was historically used to line the inside of observatory cupolas (domes), in order to absorb moisture?

texts: I was told that it was "cedar", but that is an unclear term botanically.


texts: How can I convolve a template spectrum with a photometric filter response spectrum?

texts:
Suppose I have a template stellar population spectrum (say, from Bruzual & Charlot 2003) which runs from like 1000 Angstroms to 160,000 Angstroms and which has x-axis wavelength units of Angstroms and y-axis flux density units of $L_{\odot}$ per Angstrom. Now, let's say I want to get the integrated luminosity within a bandpass that runs from $\lambda_1$ to $\lambda_2$ Angstroms, and I have another "spectrum" which gives me the filter response function for this photometric bandpass.

I know that I'm supposed to "convolve the stellar template spectrum with the bandpass response function" in order to get the integrated stellar luminosity within my bandpass, but how do I do this exactly (preferably in python)? The stellar template and filter response spectra don't have the same number of data points and are not defined on the same wavelength grid (the stellar template spectrum obviously extends much further than the filter response function).

I feel like I could interpolate the filter response spectrum onto the wavelength array of the stellar template spectrum, and assign a value of 0 to the interpolated response spectrum for wavelengths outside $\lambda_1$ to $\lambda_2$. Then I would be able to do a simple element-wise multiplication, but this does not seem like the correct approach using traditional "convolution."


texts: If the Universe is infinite, would heat death be impossible?

texts:
If the Universe is infinite, one would imagine that if we kept moving through space, we'd constantly find newer and newer galaxies and objects forever. This would imply that there is an infinite amount of matter in the Universe.

The heat death theory states that, eventually, there will be no free energy left in the Universe. Stars would no longer form, black holes would eventually evaporate, and the Universe would be effectively dead. But if there's an infinite amount of matter, won't there always be more gas clouds that haven't formed stars, more stars that have yet to become black holes, etc.? If there is an infinite amount matter and energy, shouldn't more activity be possible no matter how many stars go out or how many black holes evaporate?

One might say that with enough time, all matter in the Universe would still run dry. But if there is an infinite amount, there should always be areas in which activity is still going on...right?

Is what I'm saying correct? Does the heat death of the Universe contradict the theory that it is infinite?


texts: How has the average distance between asteroids in the asteroid belt changed over time?

texts:
Just about every webpage related to asteroids states that, on average, asteroids are about 600,000 miles apart from one another.  Have planetary scientists hazarded a guess at how close they might have been 4 billion years ago?  2 billion years ago?  200 million years?  I'm not looking for a particular age range, just an understanding of the trend over time.  Unfortunately, I'm having trouble looking up an answer to this question on my own because the keywords I've thought of keep grabbing other unrelated things
Thank you!


texts: Can we find out whether early Venus was Earth-like or not?

texts:
It has been speculated that Venus billions of years ago could've had a much different atmosphere with liquid water on its surface and possibly life. Partly thanks to the cooler young Sun. But is it possible for science to find out?

What traces would remain that our probes could measure? AFAIK Venus was completely resurfaced 300-600 million years ago so I suppose there won't be any geological signs of water of the kind found on Mars. And the atmosphere obviously has changed dramatically if Venus was once Earth-like. What should we look for to discover the evolution of Venus? What instruments should we land there, or fly in its atmosphere or orbit?


texts: Are rogue planets ever born in isolation?

texts:
I'm using the term "rogue planet" here loosely to mean anything of planet-level mass that is not orbiting around a star. Popular discussions of these objects always describe them as forming around a star and then being ejected by gravitational interaction with other planets. But I would have thought that, in principle, they could form in interstellar space just by the collapse of a sufficiently small cloud of dust and gas.

I realize that a small cloud will have less self-gravity, and would therefore take more time to collapse [see the answers for a correction to this assumption] and have a greater chance of being disrupted by other forces. But has a theoretical analysis been done of the minimum mass object that could be expected to form in isolation over the time frame of the current lifetime of the universe? It would be a surprising coincidence of that minimum threshold were the same mass as the mass required for hydrogen fusion.


texts:
The new Cosmos extra features mentions that at about 6,771,500,000 years ago the universe began an accelerated expansion. How do we know this? What evidence do we have for this renewed and accelerated expansion?

From the interactive cosmic calendar on the new Cosmos bluray, dates above taken from the heading

  Until [now], gravity has been slowing the expansion of the universe,
  but suddenly a mysterious, unknown force that we call dark energy
  takes over, the expansion of the universe begins to accelerate

How do we know it was dark energy? Given we can't define or detect dark energy, why do we believe this is the cause? How do we even know this new acceleration happened? Something in the red shift? Is there a gap in the red shift in things we can see that would imply a slow expansion and then a fast expansion? If there is a gap, why is dark energy the only explanation? Or are there other theories?

Yes that is a lot of questions, but the main question is how do we know an accelerated expansion happened at that time? the rest of the questions stem from that, mainly in asking for data to back up claims, for or against


texts: Could life survive on a planet orbiting a neutron star?

texts: Suppose an Earth-like planet orbits a neutron star, though specifically not a pulsar. Is there any possible orbit, around any possible neutron star, in which the planet could support human life?


texts: Why does earth not collide with the sun?

texts:
Gravity is most accurately described by the general theory of relativity (proposed by Albert Einstein in 1915) which describes gravity not as a force, but as a consequence of the curvature of spacetime caused by the uneven distribution of mass.(source -wikipedia)

Why it is moving on the boundary of that curvature, but not fall into the middle of that curvature and collide with sun?


texts: Has great eyesight been necessary for astronomers?

texts:
In a different (but somewhat related) field, some baseball stars have been known to have "baseball eyes." That is, an exceptional ability to visually follow the trajectory of a 90+ mph baseball to a degree enjoyed by 0.1% (one in a thousand) of the human race, as discussed in "Moneyball" by Michael Lewis.

I would imagine that would also be an advantage for an astromer, all other things being equal. But has "history"shown this to be necessary? That is, have there been a large or at least disproportionate number of famous and successful astronomers that been identified with eyesight in the top 1% (or higher) of the human population? Conversely, have there been any noted astronomers with notably bad eyesight who have made contributions because their theoretical, intuitive, or other abilities were enough to compensate?


texts: Is Earth's true anomaly roughly 1 degree currently?

texts:
I wrote software which uses GMT real time to calculate Earth's mean, eccentric, and true anomaly. I encountered a bug where after reaching 360 degrees, instead of flipping back to zero, it subtracts from 360.

So I checked Wolfram Alpha with search for Earth's true anomaly, just to see if we had passed through 0 degrees triggering the bug. As of a few days ago Wolfram and I were in agreement, approaching 360 degrees. But now Wolfram reads 179 degrees approx. I remember passing 180 in July or August.

So it appears Wolfram is also experiencing an error. To double check, true anomaly is the angle between Earth and perihelion side of major axis. We know Earth reaches its closest point to the Sun in the northern hemisphere winter, January roughly. And aphelion in summer months.

Additionally the j2000 epoch I uses 358 degrees roughly, putting the perihelion or closest approach right around early january roughly.

Thus I can only conclude Wolfram is in error as well?


texts: If the tilt of the Earth changed, would the tropics latitude change too?

texts: I wanted to know if the tilt of the earth were changed to 30 degrees would the tropics of cancer and Capricorn also both change to 30 degrees?


texts: Why can we still see 10 billion year old galaxies?

texts: I've never fully understood why we can still see galaxies that are 10 billion light years away. The age of the universe is calculated to be 13.9 billion years old and we live on a planet that it is roughly 4 billion years old. The universe came into existence 13.9 billion years ago and expanded incredibly quickly but those galaxies that were created in those early years are still visible to us via the amazing Hubble telescope (see the latest from Hubble). Those galaxies would surely have long gone so why can we still see the light from so long ago? How can we see further and further back to the beginning of the universe because surely the light from the moment of the big bang and subsequent eons would have past by us long ago?


texts: How significant is the effect of galactic rotation on line broadening of carbon monoxide?

texts:
In class the other day, we were discussing observations of rotational transitions of carbon monoxide, namely, the $J=1\to0$ and $J=2\to1$ lines. We originally had assumed that both lines would have essentially the same linewidth, but my professor then argued that the $1\to0$ transition would appear, in many cases, to be broader. His argument was this:

The $1\to0$ mode, at a rest of frequency $\nu=115\text{ GHz}$, is only half as energetic as the $2\to1$ more at $\nu=230\text{ GHz}$. As less energy is required to excite molecules from $J=0$ to $J=1$, this transition could occur in many more environments throughout a galaxy, whereas exciting a CO molecule from $J=1$ to $J=2$ requires twice as much energy and would therefore be restricted to more energetic regions, perhaps more towards the center of the galaxy. As a galaxy's rotation curve is not flat, especially in the inner regions, the $1\to0$ transition should occur at a variety of radii and therefore  a variety of tangential speeds. If we observe the galaxy edge-on, we should then expect to see more broadening of the $1\to0$ line because of this wider velocity distribution.

We've been looking for some hard numbers on this but haven't been able to find any; the argument feels slightly hand-wavy, so it would be nice to quantify this. In reality, how much broadening does the rotation of an edge-on galaxy add to the $1\to0$ transition compared to the $2\to1$ transition of carbon monoxide? How significant is this to other CO line broadening mechanisms?


texts: How long for a complete solar system cycle

texts:
Considering the solar system as a closed system, how long until all the planets pass twice by the same position relative to each other? I would say that you'd have to get the length of the year in each planet and find the lowest number that can be divided by them, is that correct or are there more things to take into account?

Furthermore, can one do this also considering the moons of the planets?

Thank you!


texts: Comparing different magnitudes. Is this statement correct?

texts:
I have two methods which allow for a detection of a signal that is at most of magnitude x. If method 2 can detect signal that are half a magnitude larger, i.e. fainter, let's say x.5 mag, is it correct to say that method 2 can detect signals that are about 60% fainter than what method 1 can detect?

Is the 60% correct? I got this number by converting the magnitudes $m_i$ to flux $f_i$, i.e.
$$100^{(m_1-m_2)/2.5}=\frac{f_2}{f_1}\approx 0.40$$
$$\Rightarrow f_2=0.40 f_1\sim 40\% f_1$$

Thus, $f_2$ is about $40\% f_1$ which means about $60\%$ fainter. I have never worked with magnitudes before, so is this a valid statement?


texts: What starting circumstances have to be for "grand tack" hypothesis to work, and why they are lacking in other planet systems(as far as we know)?

texts: I recently read a bit about "grand tack" hypothesis. It was extremely interesting and it seems to reasonably well explain many features of our solar system. At the same time it supposedly is consistent with our knowledge of other planet systems, which I don't understand. What exactly happened in solar system and at which point , that is so rare out in the other systems? Combination of Jupiter/Saturn showing up at the right places and the right time? Isn't it common that the biggest gas giants appear somewhere over the edge of frost line?


texts: Completeness detection analysis of magnitudes of galaxies

texts:
I have a magnitude from the observation. I would like to find the detection completeness of the magnitude. I want to plot the figure like this in python

How to plot the Detection completeness and magnitude of my data
import numpy as np
from astropy.table import Table
data=Table.read('magnitude_data.fits')
plt.hist('data['NB821'],bins=30)

Please let me know how to plot like this.


texts: If "9 th planet" is ejected by Jupiter or Saturn, why does it have a very far perihelion?

texts: If the "9 th planet" is ejected by Jupiter or Saturn, I think the perihelion should be near Jupiter and Saturn, but now the predicted orbit is very far away from Netpune, why would that happen?


texts: I have been trying to create a calculator which finds the distance between two stars that the user chooses. But I'm having a hard time visualizing where these stars are in real space. Do you know of any software that could actually help me crate a star map with only the stars in my calculator? I know of some star maps like Celestia, but I would like to be able to create my own map that only contains certain stars. If there isn't anything, I can find my own solution. Thanks in advance for any answers!


texts: which or what kind of star has a very stable luminosity?

texts:
I mean those kind of stars should be very stable and barely have activity.

Their light curves should be very very flat.

Our sun, as a G type star, are not so stable. At lest there are lots of floating solar spots.


texts: In the Gliese catalog there are a bunch of prefixes, such as GJ, GI, Wo, etc. My question is do the numbers overlap ever? I tried to look it up, but nothing I could find was conclusive to me.


texts:
For a design project I'm looking for elevation data for Mars' surface - the idea is to replicate a surface area of Mars as a physical model, using the elevation data to create a very rough 3d model of that particular area's topography.

Where can I find such data?


texts:
I just bought my first telescope - a Celestron CDC 1100.  It came with a 40mm lens so with a primary focal length of 2800mm the power should be 70x.

My problem is that I've looked at Sirius and Mars and they look clearer to my naked eye than with my telescope.

I am able to focus from way out so I can see the 'blind spot' of the secondary mirror, go through 'focused' and then continue moving the mirror in the same direction until I again see the blind spot.  So I know I'm focusing through when it should be 'good'.  But, like I said, what I see is a relatively unfocused spot of light that is clearer and steadier with my naked eye.

Admittedly, my 'seeing conditions' aren't very good since I am looking through my window in a suburban neighborhood where light pollution is pretty bad.  That being said, I still see Mars and Sirius quite brightly - it's just that they never come into clear focus - nor are they any larger than when I look using my eyes.  And when I move my eye around the eyepiece I see streaks of light in different directions originating from the target.

There are many stars to be seen, though they are just pinpricks as I would expect given the seeing conditions.  What I mean to say is that I cannot see all those stars with my naked eye but can see tens or hundreds more looking through the scope so I know it is gathering plenty of light as an 11" scope should.

I tried both with and without the diagonal with no discernable difference.

I have not collimated but supposedly it was collimated before leaving the factory and I would hope that even if it were off a bit from shipping I would still be able to see a sizable though fuzzy image of Mars instead of just a small speck of orangish light.

Any thoughts as to what I may have done wrong or what may be causing this lack of clarity?


texts: Why is the Sun less massive than other G2V stars?

texts:
The Wikipedia page for G-type main-sequence stars lists the expected mass and temperature for stars of each sub-classification:
$$\begin{array}{c|c|c|}
 & \text{Mass ($M_\odot$) } & \text{Temperature (K)} \\ \hline
\text{G0V} & 1.15 & 5980 \\ \hline
\text{G1V} & 1.10 & 5900 \\ \hline
\text{G2V} & 1.07 & 5800 \\ \hline
\text{G3V} & 1.04 & 5710 \\ \hline
\text{G4V} & 1.00 & 5690 \\ \hline
\text{G5V} & 0.98 & 5620 \\ \hline
\text{G6V} & 0.93 & 5570 \\ \hline
\text{G7V} & 0.90 & 5500 \\ \hline
\text{G8V} & 0.87 & 5450 \\ \hline
\text{G9V} & 0.84 & 5370 \\ \hline
\end{array}$$
Spectral type is only determined through a star's temperature, and thus the Sun with a temperature of $\text{5778 K}$ is unambiguously a G2V star.
However the Sun is noticeably less massive than other G2V stars are. Why is that? Or, another way of asking, why is the Sun hotter than other stars of the same mass (G4V)?


texts: Do the actual false colours in the M87 black hole picture convey information?

texts:
As for the title. The picture could have been plotted in grey scale, B&W, whatever couple of colours, or perhaps using a window of wavelength in order to show shift of the Doppler/relativistic Doppler kind.

Discarding the obvious dark, shall the picture be watch at merely in term of brightness, or considering yellow and red as well?

And independently, why those colours have been choose?  Just an aesthetic and suggestive choice, or that should be the apparent image as seen by eyes if we could go there?

I resume: is the picture a radio waves intensity or brightness map, or conversely a kind of "as it would be" picture in the Vis (modelled from the behaviour of the collected radio waves and theories)?


texts: Lunar Soil: what are those "bumps" and how were they formed?

texts: I was watching a video of the chinese lunar landing and saw numerous bumps in the soil. What are they? Is there any theory that explains how they came into existence?


texts: Notifier about visible ISS passes and/or Iridium flares for Ubuntu PC

texts:
I am trying to find application that would be capable of notifying me about
visible ISS pases for specified location and/or visible Iridium flares for specified location.

This software must be capable of running on Ubuntu.

I strongly prefer active open-source projects.

I know that there are multiple mobile apps but I want something that may run on Linux PC.

To avoid "this is subjective" - I will be happy about any software fulfilling this requirements and criteria are not subjective.


texts: How does a telescope measure parallax angle?

texts: I know how stars' distances are measured by using parallax, but I want to know how the actual telescope measures the parallax angle. Any helpful links/ explanations are needed.


texts: How small a star can provide Sun-level illumination to its planets?

texts:
...or how small can a solar system be, to sustain an Earth-like planet?

Sun is not really small, and 1AU is pretty far when you look at orbital radii of exoplanets and size of their stars.

How small a star can be, to still provide Earth's equivalent of 1.36 kW/m2 above its own Roche Limit (of Earth-sized planet)? What would the star's diameter and the orbit providing such irradiance be in such a case?

I guess a Brown Dwarf wouldn't be enough to give that much within its Roche Limit, meaning any planet receiving enough light would be torn apart by tidal forces, and likely stepping up to smallest Main Sequence stars would step up the energy output enough that a planet at the Roche Limit would be scorched like Mercury, so its orbit would need to be considerably larger... but I don't quite know how to perform the needed calculations.


texts: Could an object, assuming possible, escape black hole by travelling above constant speed?

texts:
I am always hearing that after travelling inside a given BH's event horizon, the escape velocity is greater than c, which makes it impossible to escape.

Suppose an ship is inside a BH. Assume it is possible to travel faster than c. If the ship applied the faster-than-light travel, would it be able to escape a black hole?

Furthermore, it seems to me that above event horizon, the escape velocity is less than c, while inside event horizon, the escape velocity is greater than c. This leads to a further question: Does the escape velocity increase the closer you get to a BH's singularity?


texts: Historic observational data - position of the planets

texts:
Is there an online source where historic observational data regarding the position of the planets can be found? I was always intrigued by the fact that Neptune was mathematically predicted before it was actually observed (wiki article).

I am curios in finding more about this mathematical prediction regarding the existence of Neptune. Here are a few questions related to this:

Are there any detailed references on the subject?
Is it possible to find the data which lead to this discovery online somewhere?
Are there online resources regarding the position of the planets (now or at various points in the past)?


texts: Could the largest SMBH swallow an entire galaxy?

texts:
It is unlikely that the largest supermassive black hole in the universe has already been discovered, there may be much larger ones.

Are there, or could there be, supermassive black holes large enough to swallow whole galaxies as opposed to the occasional star?

Are there other factors beyond size that would also affect a SMBH's ability to swallow it's own galaxy?


texts: Why do CME's "zig-zag" on their way to Earth?

texts:
This answer to When a coronal mass ejection (CME) hits a spacecraft, from which direction will the particles come? states:

A single CME will impact a spacecraft from only one direction, but that direction might not be directly from the sun because a CME may zigzag en route.

Looking at that link, the cause of the zig-zagging is still unclear to me

One of the first things they noticed was how CMEs trying to go "up"—out of the plane of the solar system and away from the planets—are turned back down again. Gallagher confesses that they had to "crack the books" and spend some time at the white board to fully understand the phenomenon. In the end, the explanation was simple:

The sun's global magnetic field, which is shaped like a bar magnet, guides the wayward CMEs back toward the sun's equator. When the clouds reach low latitudes, they get caught up in the solar wind and head out toward the planets—"like a cork bobbing along a river," says Gallagher.
Once a CME is embedded in the solar wind, it can experience significant acceleration. "This is a result of aerodynamic drag," says Byrne. "If the wind is blowing fast enough, it drags the CME along with it—something we actually observed in the STEREO data."

Question: I can't find an explanation here that I can sink my teeth into. Is it possible to explain in a more scientific way? What is the restoring force that would bring a wayward CM back towards the plane exactly? Is the zig-zagging only in the out-of-plane direction?


texts: Stars have in the past passed within 1 light year from the Sun, and will do so in the future too. If they have Oort clouds, would there not be interactions between their Oort cloud objects and the planets of the Solar system? For example, the outer edge of the Sun's Oort cloud is approximately 100,000 AU away. So, if another star comes at a distance of 1 light year from the Sun, its Oort cloud should similarly go through the inner solar system. Does this actually happen?


texts: A few days ago, I took a photo of the night sky in the mountains of Georgia with my DSLR. There, I noticed that one single star (in the center of the part of the photo that I added below) looks very different than all the other stars on the photo. Why does it have this white glow?


texts: Why do PMS stars on the Hayashi track remain at a constant temperature while they contract?

texts:
Why do pre-main-sequence stars on the Hayashi track remain at a constant temperature while they contract?

I've read the Wikipedia article, so no need to repeat the derivation.

What I took away from that is that the extra heat generated by contraction is given off almost exactly because the whole star is convective and the atmosphere is very capable of radiating that heat away if the opacity is mainly caused by hydrogen ions, which is the case in the cooler of the pre-main-sequence stars.

Is that correct?


texts: Why does the Solar Wind consist of charged particles?

texts:
The Wikipedia article on Solar Wind gives the following explanation:

  The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between 0.5 and 10 keV.

If the solar wind consists of both electrons and protons, why don't they combine and give Hydrogen or any other elements? Then, why would Solar Wind be charged? Is that because of the high kinetic energy of the ejected particles? If yes, let us consider a proton and an electon. They must be of almost the same energy if so there will be no relative kinetic energy, so I think they must combine in the same way as if they were at rest or in motion at small velocities.


texts: How did Batygin estimate when Planet Nine was ejected?

texts:
Konstantin Batygin has estimated that if Planet Nine was ejected, it would have been ejected 3-10 million years after the formation of the Solar System.

I'm curious as to how he arrived at this figure. Was it through simulations of the early Solar System, a prediction of the alignments of orbits at that time, or something completely different?


texts: What exactly would the resolution of an exoplanet hypothetically imaged by using the Sun as a gravitational lens be?

texts:
This video talks about how by sending a spacecraft to around 600 AU and beyond, we would could use the Sun as a gravitational lens and take clear detailed images of exoplanets light-years away.
What it doesn't say however is the exact resolution. An exoplanet 4 light-years away would obviously appear bigger and more detailed than one 100 light years away. But by how much?
Is there a direct formula showing the resolution for an exoplanet at x light-years? As in kilometers/pixel?


texts: Could population III stars develop directly into population I stars?

texts: Hundreds of millions of years after the Big Bang, the very first stars began to form consisting of mostly hydrogen, a bit of helium, and maybe some lithium. These stars lacked any "metals" (elements heavier than helium) and are categorized as Population III stars. We have yet to observe any of these Pop III stars, and observation remains unlikely. The reason for this is because Pop III stars are thought to have been incredibly massive, so they died out so long ago that we can no longer see their light. Pop I stars are metal-rich; their metallicity is 1/10 to 3 times that of our Sun's. In my research, everyone seems to agree that that the first generation of stars had no metal, second generation stars had very little, and third generation stars have some metal.But, no one ever addresses the possibilities. So, is it possible that some Pop III stars were so massive that they were able to skip Pop II and go straight to Pop I? Maybe if several are close by when they go supernova?


texts: Where do the photons come from at the edge of an Event Horizon?

texts:
I was reading about Professor Finkelstein's speech at Cambridge University back in the 50's. He was explaining the dual reference frame of a black hole's event horizon.  (A person falling in has one reference frame, and a person watching has a second.).... This I understand.  My question is about the person watching reference frame...
It is my understanding that a person watching someone fall into the black hole would never actually see the person disappear.  My question is how is this possible?  THe photons coming from the person at the edge of the event horizon are only given off while the person is on this side of the EH.  Once the person crosses the horizon, then the photons should not be there anymore for me to see. I know that time is slowed... but if I stared for 1000 years would I ever see the person cross the threshold?  If not, where are these photons coming from?


texts: SDSS Image FITS files have negative values. What do these negative values mean?

texts: I am new to using SDSS image files and have noticed that some of the values in the FITS file are negative. Can somebody explain to me what these values actually mean?


texts:
If given the sidereal day, is it possible to derive the synodic day of Earth? If a derivation is possible, could anyone illustrate it or point me in the right direction?
Wikipedia's Synodic day begins:

A synodic day is the period it takes for a planet to rotate once in relation to the star it is orbiting (its primary body).

Question: How can one calculate that?